Transgene integrity, chimerism, silencing and stability in rice

Transgenic rice plants containing proteinase inhibitor (pin1 or pin2) or Btt cryIIIA genes were produced by transformation based on direct DNA delivery. Genomic DNA blot analyses revealed that a majority of the transformants contained multiple, often rearranged, copies of the transgene. An investigation into the structural integrity of transgenes revealed that several transformants that contained multiple fragments often lacked an intact, functional transcriptional unit. Several low copy transformants also did not contain an intact copy of the transgene due to fragmentation of the 35S promoter, suggesting an inherent susceptibility of this promoter to breakage. Chimerism, i.e. the presence of transgene only in some, but not all, tillers was observed in several primary transformants, indicating that this could be one of the causes behind the observed cases of non-Mendelian segregation. The phenomenon of transgene silencing was observed in a rice line containing a complex transgene locus introduced by biolistics. Although both the transgenes, i.e. Btt cryIIIA and bar were functional in the primary transformant, their expression in selfed (R...